The present invention relates to unwinding arrangements for weblike material.
On unwinding a weblike material such as a packing material web, packing material strip or any other flexible, elongated material from a roll, it is of great importance that the roll rotates in such a manner that exaggerated tractive stresses or jerks are not applied to the material. In the case of large material rolls of appreciable dimensions and weight, brakes of the electrical or hydraulic type are used which are controlled in such a manner that the unwinding resistance during the whole time is kept at a suitable level. With smaller, relatively light rolls, e.g. material strips, it is customary for reasons of cost to use relatively simple devices. Such a device may be a friction brake in contact with the roll which may have a lever which acts upon the outgoing material strip so that the braking force increases when the tractive stress in the material strip diminishes. Such an arrangement is used in the unwinding of so-called longitudinally jointed strips of plastics on packing machines of the type which convert a tube made of packing material to individual packing containers. This arrangement comprises a brake appliance of rubber resting against the peripheral edge of the roll, which in the case of small rolls and a relatively uniform rate of unwinding, provides the required braking, but cannot function satisfactorily with heavier rolls and varying rate of unwinding. This design, moreover, has the disadvantage that the wear on the rubber surface of the brake appliance is relatively high which may cause fouling, requires frequent replacement of the brake appliance.